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H7N9, the newly identified avian influenza strain that has so far infected scores of people and killed more than 20, passes between birds and humans more easily than the H5N1 strain that surfaced in 2003, according to the World Health Organization. After a weeklong investigation, a team of global researchers believe exposure to live ducks and chickens at poultry markets is associated with transmission. Of concern is the fact that birds generally don't display clear symptoms, but closing some poultry markets appears to have decreased new human cases.

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Veterinarian Jurgen Richt and disease expert Wenjun Ma developed poultry vaccines that protect against H5N1 and H7N9, two zoonotic influenza strains responsible for the deaths of hundreds of people and thousands of birds across Asia. The team created two vaccines by combining each strain with Newcastle virus and found the vaccines protected against the corresponding influenza strain as well as Newcastle disease. Ma said the approach could be used to develop a vaccine for the H5N2 virus ravaging farms in the Midwest.

A hunter-killed green-winged teal from Washington state was infected with a form of H5N1 avian influenza, according to test results. The duck is the first case in the U.S. The strain shares characteristics with the H5N1 virus that has caused human infections in Asia and Egypt, as well as with H5N8. At this point, the findings show migratory birds are transmitting disease, and poultry is the main concern, according to experts. For humans, "I would say the risk is not zero," said U.S. Geological Survey microbiologist Hon Ip.

The National Veterinary Services Laboratory has detected a case of H5N8 avian influenza in an American wigeon duck from Utah. The disease is highly pathogenic to poultry. "This event underscores the importance of biosecurity for backyard bird owners," said acting state veterinarian Warren Hess. "We strongly encourage owners to eliminate any contact between their birds and wild birds. We also want them to monitor their flock closely and report sick birds." While the H5N8 strain hasn't been known to infect humans, hunters are cautioned to handle fowl with gloves and to disinfect all surfaces and tools.

Chinese health officials have confirmed a human case of H10N8 avian influenza. A 73-year-old woman died Dec. 6 after being hospitalized Nov. 30. H10N8 was identified among poultry market birds in 2012 and in wild birds in 2011. This is the third avian influenza virus known to have jumped from birds to humans this year, joining H6N1 and H7N9, the latter of which is still circulating and has killed 45 people among 142 known infections.

Chinese scientists report that ducks are the link between chickens and the H7N9 avian influenza virus that has so far sickened 133 people, resulting in 43 deaths. The study interpreted genetic data from 1,341 birds of various species as well as water and avian fecal samples from poultry markets. Additionally, the scientists identified a novel avian influenza strain, H7N7. "The discovery of a novel H7N7 lineage that can infect ferrets reminds us that even if H7N9 does not return, there are risks lurking amongst the great diversity of avian influenza viruses," the scientists wrote.